ISO
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION

DIN
DEUTSCHES INSTITUT FÜR NORMUNG (German Institute for Standardization)

DIN EN 12756 (24960)
In conjunction with the INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) and its applicable standard (ISO 3069), the German Institute for Standardization (DIN) has issued suggested guidelines for mechanical seals in standard DIN EN 12756 (24960).
The standard contains guidelines for seal chambers, main dimensions, designations and material codes.
However, the standard does not prescribe the actual design of mechanical seals.

Excerpt from EN 12756 (24960)

Single mechanical seal, Form U, unbalanced	Single mechanical seal, Form B, balanced
Double mechanical seal, back-to-back, Form U, unbalanced	Double mechanical seal, back-to-back, Form B, balanced

However, these standards definitely do not reflect the current state of technology!
If users take DIN / ISO criteria as a guideline, the seal selection decision will be based on totally outdated information, and as a result unnecessary faults and downtime can occur during ongoing operation. The user can be faced with excessive maintenance expenses as well as other avoidable costs.
For this reason, we would like to highlight some important criteria over and above the DIN standard which should be taken into account during selection and specification of a mechanical seal and which can drastically reduce failure rates and operating costs.

DIN EN 12756 (24960)	One step ahead with DEPAC
Mechanical seals are still produced, specified, sold and installed as “balanced” or “unbalanced” versions.	However to maximize the life of the seal, you should only use balanced versions wherever possible. These version are not more expensive to produce, and they can be supplied at prices which are comparable to the price of unbalanced seals in the same series (DEPAC Type 186, 196).
A stepped sleeve or shaft is the only design option which is offered for balanced mechanical seals. There should be no need for a sleeve at all, and this specification actually creates the need for a second sleeve design feature on balanced seals.	Balanced mechanical seals can be produced without the need for a sleeve and/or stepped sleeve (DEPAC Type 186, 196).
Dynamic designs are still recommended as the standard solution for single seals, and this is reflected in the dimension specifications.	Stationary seals are always the better option. They are normally in the same price category as dynamic seals, and they offer superior operational reliability (DEPAC Type 191, 196).
The DIN specifications include mechanical seals which have the spring located in the medium.	When the medium contains solids, clogging can occur at the spring, causing early failure of the mechanical seal. To avoid this problem, we recommend that the spring elements on mechanical seals should be located outside of the pump medium wherever possible (DEPAC Type 186, 196).
The standard does not mention that many dynamic mechanical seals damage the pump shaft or sleeve which then has to be replaced on every repair call at considerable expense. As a result of this “omission” in the standard, a thriving spare parts industry has developed at the users expense.	For cost reasons DEPAC recommends that mechanical seals should always be selected as types which eliminate the risk of damage to the shaft or protective sleeve (DEPAC Type 186, 196). The price difference is minimal, and eliminating the risk of shaft and sleeve damage can produce huge savings.
People still continue to recommend conventional mechanical seals rather than cartridge seals.	To make mechanical installation easier and avoid installation errors, cartridge seals should be used wherever possible. Only the initial price is higher. Repair and spare part costs are comparable to conventional mechanical seals (DEPAC Type 270).
DIN 24960 recommends, for example, back-to-back double seal configurations which are completely outdated.	To maximize operational reliability, we recommend double mechanical seals with a tandem-active stationary cartridge design and double pressure balancing (DEPAC Type 322).
Standard update DIN 24960 C (cartridge) is complicated and awkward.	DIN guidelines make cost-effective production of mechanical seals difficult. DEPAC has proven that technically sophisticated cartridge seals can be produced simply and at an affordable price (DEPAC Type 323).
According to the standard, the seal chambers for mechanical seals should be as confined or nearly as confined as for stuffing boxes.	For optimal operation, the diameter should be significantly larger for mechanical seals. API 610 / 682 specifications and ANSI have reflected this fact for a long time, and the technical recommendations they contain are currently state of the art.

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